Hey Bean... Thanks for the info. The plumbers putty would work better I agree. However I did not have any laying around and the duct tape works great if you take your time and press it down well all around. When cutting the hole in the pictures (50g sump) I actually was more concerned with the photo taking that I did have a little bit of a leak. No big deal. The last 4 holes that I have cut I did better with the duct tape and did not have any leaking cooling water at all.
